In order to maintain the highest service quality and continuity for a wireless user, user equipment (UE) will not only maintain a connection with its serving cell, but also monitor neighboring cells. A UE will typically perform mobility decisions, such as handover and cell reselection, towards base stations in the same radio access technology (RAT), but also towards additional networks or RATs. Accordingly, a UE (and one or more network entities) often monitor and evaluate serving cell quality, initiate periodic cell search activity for candidate neighbor cells, perform various measurements regarding neighboring cells, and perform mobility evaluations, e.g., determining whether the UE should move to another serving cell.
If a better serving cell than the current serving cell is identified, handover to the other cell can be initiated. The handover can be requested to, for example, the same carrier (intra-frequency handover), to cells on other carriers (inter-frequency handover) and to other cells of a different RAT (inter-RAT handover). The handover itself may consist of multiple steps, such as a handover initiation followed by radio link establishment with the target cell. This process may be understood, for instance, with respect to the exemplary signal flow illustrated in FIG. 1.
Referring to the example of FIG. 1, an IRAT handover procedure is initiated upon the reception of a measurement report 102 by a radio network controller (RNC), for instance a serving RNC (SRNC), from a UE in a Cell-DCH state. The measurement may be, for example, a 2d or 6b measurement report according to a Radio Resource Control (RRC) protocol. After evaluation of the measurement report 102, the link may be placed into a Compressed Mode Control state, which places gaps in the downlink and uplink transmissions, allowing the UE to perform measurements on neighboring cells. If the measurement report 102 indicates that the current frequency is below an acceptable threshold, the RNC can send a measurement control message 104 to the UE to start measurements on listed neighboring cells. For instance, in the case of an inter-RAT (IRAT) handover, such as from Universal Mobile Telecommunications System (UMTS) to Global System for Mobile Communications (GSM) RATs, the UE may start measurements on neighboring GSM cells. When the 3a criteria are fulfilled, the UE sends a measurement report 106, including the measurements on the neighboring GSM cells, to the RNC. The RNC evaluates the report and proceeds with the execution of the IRAT handover.
To execute the handover, the RNC sends a relocation required message 108 to the Mobile Switching Center (MSC) to request handover to the GSM network and starts a timer, Trelocprep. In the example of FIG. 1, the message 108 contains identification of the target cell, information about mobile capabilities, and security information. The MSC generates a handover request message 110, which is sent to the target base station sub-system (BSS). When the BSS receives the handover request message 110, it takes the necessary actions to allow the UE to access the radio resources of the BSS. Once resource allocation 112 has been completed, the BSS returns a handover request acknowledgement 114 to the MSC. A relocation command 116 will then be sent by the MSC to the RNC. The RNC stops the timer Trelocprep and starts the timer Trelocoverall, and upon receipt of the relocation command 116, sends an RRC handover from Universal Terrestrial Radio Access Network (UTRAN) command 118 to the UE, which contains the Handover Reference number previously allocated by the BSS. The RNC may also include which Radio Access Bearers (RABs) are handed over to GSM in the handover message.
The UE can then access the new radio resource using the Handover Reference number contained in the handover access message 118. The target BSS uses this reference number to ensure that the correct mobile device is accessing the system for handover. Accordingly, the BSS may send a handover detect message to the MSC. When the UE is successfully communicating with the BSS, a handover access/complete message 120 will be sent by the UE to the BSS, which will in turn send a handover complete message 122 to the MSC. The MSC will then initiate an IU Release Command 124. The Trelocoverall timer is stopped as the IU release command is received by the RNC, according to the Radio Access Network Application Part (RANAP) protocol. Radio links used by the UE can then be deleted on the UTRAN side.
However, existing implementations fail to provide intelligent handover requests and processing that can accommodate certain scenarios discussed herein.